Is there any way to make multiple objects convex hulls?
Use the bmesh operator
Use the bmesh convex hull operator as outlined here https://blender.stackexchange.com/a/121815/15543
Test script, run in object mode. Turns all selected mesh objects into their convex hull.
import bpy
import bmesh

context = bpy.context

meshes = set(o.data for o in context.selected_objects if o.type == 'MESH')

bm = bmesh.new()
for me in meshes:
    bm.from_mesh(me)
    bmesh.ops.convex_hull(bm, input=bm.verts)
    bm.to_mesh(me)
    me.update()
    bm.clear()